HTML (Hypertext Markup Language)
HTML is the language of the web and hence you must understand it if you want to build your own websites. An investment in learning HTML is very rewarding and it will allow you to understand much of how the web works. This is also a must have skill if you want to do your own Search Engine Optimization (SEO).
CSS (Cascading Style Sheets)
CSS or Cascading Style Sheets is the next skill you should master. CSS is quiet easy once you take the time to understand how it works. CSS makes changing the style used on your websites easy. in addition a good knowledge of CSS will allow you to minimize the number of graphics or photos you need on a website and it will still look good.
Your website needs to look good so you need to have a good understanding of web graphics. If you decide to produce your own make sure that you don't overdo the number of graphics on your website and also be warned that its very tempting to spend too much time making your graphics look better than they really need to be. Keep it simple.
In addition to the above 3 essential skills one or more of the following will be needed for the more complex sites:
-interact with users
-validating user input to forms
PHP is a scripting language that is used to create dynamic websites. The best way to explain this is via an example:
One typical and very powerful use of PHP is to personalize sales pages. For example lets say you have a squeeze page (explained in sales process section) offering a free demo of your product. When the user enters their name and email address into the form on the squeeze page you can have a php script (program) that reads the persons name and then uses it on any following pages that they see. When done well this is very impressive to your website visitor.
PHP is also a great tool to use to interact with a database on your website. A simple example would be where you have a membership website that requires members to log in every time they use the website. The members username and password are stored in the database and the login page uses a php script to check that the username and password are valid.
If your website needs a database them MySQL is a good option. Its free and integrates well with PHP. WordPress uses both PHP and MySQL so if you are a WordPress user any knowledge of PHP and MySQL will come in useful – though for most uses you won't need any detailed knowledge.
I hope this is useful and helps you to decide what skills you need to brush up on for your web or blog development.